Abstract - Copeia, 1997

Offspring size at birth is assumed to be an important determinant
of initial success in a variety of organisms. For natural selection
to be effective at modifying offspring size at birth in a given
population, there must be some level of additive variation for
birth size. In ovoviviparous fish, initial offspring size appears
to be entirely under maternal control, and thus any differences
in birth size among offspring within females is not due to selectable
genetic variation. However, additive genetic variation may exist
between females due to genetic differences in allocation patterns
to their offspring. Such "grandfather effects" have
been suggested for mosquitofish (Gambusia spp.), though
actual estimates of heritability have not been previously published.
Herein, we used a two generation full-sib/half-sib breeding design
to estimate levels of additive genetic variation among "grandfathers"
in a population of Gambusia holbrooki. Significant genetic
variation was not detectable for fathers, as was previously suggested
(Reznick, 1981). However, detectable genetic variation was found
at the level of grandfathers, with an estimate of heritability
of approximately 7%. This level of heritability is consistent
with other estimates of life history characters in many other
species, and suggests that there is sufficient additive genetic
variation for this important life history trait in natural populations
of mosquitofish.

Last Updated : 6/12/98
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